Two methods of making “structured” drawn glass, having micro- or nano-channels in the direction of the draw are commonly known and used. The first method is to start with a preform that contains two kinds of glass. The core glass is easily etched in acid, while the cladding is not etchable. The preform is drawn into fiber, cut into pieces, and the pieces are bundled together in parallel. This drawing and bundling can be repeated many times. Finally, the last bundle is sliced perpendicular to the drawing direction into typically 1 millimeter thick wafers and the core glass is etched out from both sides leaving an array of holes. The difficulty is that the cut wafer, if more than a few millimeters thick, the etching process takes a prohibitively long time, since the core glass is etched out through increasingly long, narrow channels. The product produced is known as microchannel or microchannel glass.
The second method is used to make structured optical fiber (also known as photonic crystal fiber or holey fiber). In this case, the preform has holes through it which can be produced by bundling solid and hollow rods or by bundling two kinds of glass, fusing and etching out one glass (Falkenstein, et al, Optics Letters vol. 29, p. 1858, 2004). In either case, the preform has holes through it when it is ready for drawing. The preform is then drawn once or repeatedly to make the fiber. The difficulty is that the holes tend to collapse and/or distort during the drawing process. The method is very sensitive to drawing conditions, and it is difficult to make specimens that have no significant distortion.